This invention relates to a technique and a related device for preventing the formation of blood clots in intravenous catheters.
In an intravenous feeding assembly, an intravenous catheter is inserted into a person's vein and connected at a proximal end to an intravenous tube extending from a liquid supply. Frequently, intravenous lines are lost because the monitoring personnel forget to change the infusion bag and a clot forms in the catheter. In patients who have accessible veins, the intravenous line has to be restarted by a physician or a nurse specialist. Precious moments can be lost while the physician or nurse specialist is being sought. During that time, the patient does not receive intravenous fluid and does not have an intravenous line.
In addition, there are a large number of cases in which no further veins are accessible. In such cases, another intravenous can be started only with great difficulty, for example, by having a surgeon cut into a vein. In this group of patients, the maintenance of an intravenous line is especially crucial.
Intravenous lines are particularly critical for certain kinds of patients. For example, after a myocardial infarction, a patient's myocardium is irritable and the patient can go into a life-threatening arhythmia such as ventricular fibrillation. During that time, if there is no available intravenous port, intravenous medication cannot be injected and the patient dies. Also, when the patient is in ventricular fibrillation, it is extremely difficult to obtain venous access because blood is not being efficiently pumped. The absence of an intravenous line in the patient at that time can be a direct cause of death.
Patients who are bleeding and are receiving blood represent another critical group. When the intravenous line becomes clotted and the line is lost, it is again difficult to obtain venous access. Such a patient can bleed to death or exanguinate, if there is no readily available intravenous line.
Another critical group is patients who have a severe, life-threatening infection requiring the continuous or continual supply of antibiotics. In such cases, where the intravenous line is clotted and a physician or nurse specialist cannot be found, the patient can die.
In yet another critical group, the patients have a pulmonary embolus and require continuous heparinization. In such a patient, a clot in an intravenous line causing an interruption in the heparin flow of only a few minutes can result in the formation of another pulmonary embolism and instantaneous death.
Other consequences of interruption of intravenous lines include the prodding, bruising and pricking of unfortunate patients. For old people, especially, the restarting of intravenous lines is a constant source of pain and suffering.
Devices are known which generate an alarm, e.g., an audible signal, upon the exhaustion of an intravenous supply or the formation of a blockage in the intravenous flow path. Such devices typically include a photoelectric drip sensor which monitors fluid flow in an intravenous line. Upon a cessation of fluid flow, the photoelectric sensor triggers the alarm. It is to be noted that care-takers are frequently unavailable at the time an intravenous supply runs out and an alarm sounds.
Heparin is an anticlotting compound and is provided in catheters which are inserted intravenously for enabling periodic access to a patient's blood or circulatory system. Inasmuch as such catheters are closed at a proximal end, for example, by a self-sealing polymeric membrane, the heparin remains in the catheter owing to suction forces. Such a device is known as a heparin lock.
U.S. Pat. No. 5,195,967 discloses a method and apparatus for automatically activating or instituting a heparin lock upon an automatic detection of at least a partial cessation of fluid flow along an intravenous flow path. In one mechanically implemented embodiment, the apparatus is responsive to a pressure drop along the intravenous flow path at an intravenous catheter. However, it has been discovered that the pressure sensing approach is not easily adapted to all cases. Specifically, the catheter diameter and the intravenous flow rate, as well as the materials and design of the sensing components, must be delicately matched to ensure heparin lock activation upon a termination of intravenous flow due to exhaustion of an intravenous fluid supply.